Recently, as integration density of a memory improves, occurrence possibility of a soft error in a memory increases. Thus, in order to solve this problem, importance of an error check and correction memory has increased. A soft error may occur due to electromagnetic interference, static electricity, a cosmic ray and others. For example, a soft error may occur due to a charge generated by ionization radiation.
For example, where α (alpha) particles penetrate a 3D memory having high memory integration density, the α particle generates an electron-hole pair near a memory cell. Then, if an amount of a charge of the generated electron-hole pair exceeds a certain threshold value, the a particles may become a cause for a bit error. Further, as integration density of a memory increases, occurrence possibility of a fault of a memory cell in a 3D memory may also increase.
Error check and correction within a memory for checking and correcting an error occurring within a memory are carried out through an error correction code. In order to overcome an error occurring in a memory, the error check and correction are necessary. Thus, error correction codes of a memory such as a SEC-DED code and a SEC-DED-DAEC code have been essential for design of a memory.
In order to overcome limit of storage capacity of a memory, research on a 3D memory has been actively conducted for recent years. A 3D memory, in which a multiple number of memory layers are stacked, has had a problem since a soft error will be highly likely to occur in an upper memory layer among the multiple memory layers. This is because most α particles crash onto the upper memory layer first among the multiple stacked memory layers, and the upper memory layer protects lower memory layers from the α particles.
Further, reliability of the 3D memory, which has recently attracted interests, is determined mainly by reliability of an upper slice, and a method for improving error check and correction performance of the upper memory layer of the 3D memory is necessary.